An ab initio investigation of groups III-V monochalcogenides

Two-dimensional (2D) materials have attracted a great attention due to their unusual properties such as high degree of anisotropy and chemical functionality over relatively large areas. Since the graphene breakthrough, a variety of 2D materials have been predicted, synthesized, and characterized, the most prominent family being the transition-metal dichalcogenides, e.g., MoS₂, WSe₂, etc, representing semiconductors and topological semimetals. Inspired by the chemical flexibility and possible crystal structure variety, we consider the family of 2D monochalcogenides of the type MQ, where M = Al, Ga, In, Si, Ge, Sn, P, As, Sb; Q = S, Se, Te. Using density functional theory within the generalized gradient approximation (PBEsol) and hybrid functional calculations, we explore the possible crystal structure and electronic properties of this family of 2D MQ. For each compound we consider 12 crystal structures differing on space group, chemical bonding, and coordination, analyzing their electronic structure, band gaps, work function, and structural stability in terms of phonon spectra. The properties of these 2D materials are then compared to their 3D bulk parent structures, and a classification in terms of metallic versus semiconducting character, bonding and coordination is provided.